At the downtown stations people about to board heed the instructions on the train doors stand to the side of the doors and additionally do the intelligent thing and stand close to the train on the platform so the people exiting the train aren't blocked and people moving down the platform from other cars aren't blocked either. By Broadway this degrades to people waiting well back from the doors as instructed, which is fine for people to step off the cars, but creates a series of obstacles for for people trying to get to the exits after getting off the train. Beyond Broadway Station people are crowding right up to the doors before they open, often requiring the liberal use of shoulders and elbows to get off the train.
At first I thought it was just a side-effect of a reverse commute, when people boarding the aren't really expecting people to be exiting the train, but it's not the case. For one, when I get off at Lougheed, the people I have to push through are on their way from Coquitlam to New Westminster or Surrey, which is an even stranger commute. I've also been watching it happen with the outbound trains in the evening when the trains are packed to the gills and scores of people exiting at the suburban stops, yet those boarding insist on standing completely in the way. It's like there is some unwritten rule that SkyTrain etiquette does not apply beyond the original 1986 Broadway-to-Waterfront run. I really don't get it.